He was Cardinal-Nephew to Pope Alexander VII and became a powerful political force inside the Roman Catholic Church during the latter half of the 17th century.

In 1659, at the death of Cardinal Luigi Capponi, Chigi was appointed Librarian of the Holy Roman Church and held the role for several years.

Following the death of his uncle, he oversaw the creation of the tomb for Alexander VII, designed by Gianlorenzo Bernini.

Another influential person was Dean of the College, Francesco Barberini, who was leader of the group of old cardinals created by his uncle Pope Urban VIII.

The French party was instructed to work for the election of cardinal Secretary of State Giulio Rospigliosi.

Initially Chigi, supported by the Spanish party, proposed to elect cardinal Scipione d'Elci, but was not able to secure for him the required majority of two thirds.